Field of the Invention
The present invention relates to a tool exchanger apparatus of a machine tool for indexing a tool by turning motion of a turret.
Description of the Related Art
A tool exchanger apparatus for automatically changing tools mounted on a main shaft of a machine tool is conventionally used. A plurality of tools required for an operation is set, in advance, in the tool exchanger apparatus, and the tool mounted on the main shaft of the machine tool is automatically changed to another tool designated in accordance with a machining state.
In such a tool exchanger apparatus, the tools are conveyed by the turning motion of the turret, but when the turning motion is carried out for conveying the tool, it is necessary to prevent the tool from falling off.
Hence, the following techniques to prevent a tool from falling off are known.
Japanese Patent Application Laid-Open No. 8-115113 discloses a technique in which a machine tool includes a weight data storage, weight data of tools which is input by a data inputting portion is stored in the weight data storage, and an operation of a turret of the machine tool is controlled based on the weight data.
Japanese Patent Application Laid-Open No. 2005-205503 discloses a technique in which, when a turret which conveys a tool of a machine tool is turned, a centrifugal force applied to the tool is estimated, and a maximum turning speed is determined based on the estimated centrifugal force and a gripping force on the tool in a tool gripping portion of the turret.
According to the techniques disclosed in Japanese Patent Application Laid-Open No. 8-115113 and Japanese Patent Application Laid-Open No. 2005-205503, by appropriately setting the turning speed of the turret at the time of the indexing operation of a tool based on the weight data of the tool and the centrifugal force applied to the tool, it is possible not only to prevent the tool from falling off, but also to shorten a tool changing time. According to the techniques disclosed in Japanese Patent Application Laid-Open No. 8-115113 and Japanese Patent Application Laid-Open No. 2005-205503, however, the turning speed is constant with respect to a weight of a tool on the turret. However, when a turning axis of the turret inclines with respect to a vertical direction, a direction with respect to the axis of a weight applied to the tool changes in accordance with a turning phase of the turret. Accordingly, if the turret is turned at a constant speed, there may be a margin with respect to a limit speed of a turning motion depending upon the turning phase, resulting in insufficient reduction in tool changing time.